In many body tissues, activity of individual cells, especially contraction, is initiated by changes in trans-membrane potentials. These types of tissue are also called excitable tissue, since when they are excited by an electrical signal, they react by activation. Some examples of excitable tissue include: cardiac muscle, skeletal muscle, smooth muscle and neural tissue. In many cases, the activity of large numbers of such excitable tissue cells is synchronized by propagating electrical activation signals. An activation signal is an electrical signal which, when it reaches an excitable cell, causes it to depolarize and perform its activity. In addition, the depolarization creates a new propagating activation signal which then continues to propagate towards the next un-activated cell. In most excitable tissue, the cell is refractory after a depolarization, such that the activation signal cannot immediately travel backwards.
The gastrointestinal (GI) tract is an example of a major physiological system in which many activities are coordinated by propagating electrical activation signals. The GI tract comprise a stomach, a small intestine and a large intestine. In a typical digestive process, food is chewed in the mouth and enters the stomach for digestion. The food is periodically passed to the antrum for grinding down and then passed back to the stomach. After a period of time, the pyloric sphincter opens and the food is passed to the small intestine. In the small intestine the food is churned and passed forward by a rhythmic motion of the intestines, until it reaches the large intestine. A one way sphincter allows movement only from the small intestine to the large intestine. Once in the large intestine, the food is further churned and compacted by motions of the large intestines. These motions also advance the digested food, now feces, to a pair of outlet sphincters, which mark the end of the GI tract.
The GI tract is mostly composed of smooth muscle, which, when depolarized, contracts. All of the above described movements of the GI tract are synchronized by propagating activation signals. As can be appreciated, in many cases, these electrical signals are not properly activated and/or responded to, resulting in disease. In one example, an ulcer causes inflammation of GI tissue. The inflamed tissue may generate spurious activation signals, which can cause the stomach to contract in a chaotic manner. The inflamed tissue may also affect the activation profile of the stomach by not conducting activation signals or by having a different conduction velocity than healthy tissue.
Pacing the GI tract is well known in the art, for example as shown in U.S. Pat. Nos. 5,292,344 and 5,540,730, the disclosures of which are incorporated herein by reference. The '730 patent describes both increasing and decreasing the excitability of the GI tract by stimulating different portions of the vagus nerve. The '344 patent describes a pacemaker which directly stimulates portions of the GI tract. Electrical stimulation of the GI tract is also known to be used for stimulating the GI tract of patients suffering from post operative damping syndrome, as evidenced by SU 1039506, the disclosure of which is incorporated herein by reference.
The uterus also comprises smooth muscle, which contracts in response to electrical activation signals. “Uterine Electromyography: A Critical Review” by D. Devedeux, et al., Am. J. Obstet Gynecol 1993; 169:1636–53, the disclosure of which is incorporated herein by reference, describes the different types of uterine muscle and electrical signals generated by such muscles. An important finding which is described therein is that electrical activity in the uterus appears to be uncorrelated prior to labor, but when labor is established, the contractions and the electrical activity associated to them become highly synchronized.
In current medical practice, labor can be delayed by administering certain drugs. However, the operation of these drugs is somewhat uncertain. In addition, labor can be induced using other drugs, such as Oxytocin. Unfortunately, the dosage of Oxytocin which is required cannot be known in advance and overdoses of the drug can result in over-contraction which can mechanically damage the fetus and/or the mother.
SU 709078, the disclosure of which is incorporated herein by reference, describes stimulating the uterus after labor using an externally applied electrical current, to increase the contractions and aid in the expulsion of the afterbirth and reduce bleeding by rapidly shrinking the uterus.
The use of locally applied electrical fields for reducing pain is well known in the art. “Electrical Field Stimulation—Meditated Relaxation of a Rabbit Middle Cerebral Artery”, D. A. Van Ripper and J. A. Bevan, Circulatory Research 1992; 70:1104–1112, the disclosure of which is incorporated herein by reference, describes causing the relaxation of an artery by applying an electric field. U.S. Pat. No. 4,537,195, the disclosure of which is incorporated herein by reference, describes treatment of pain using TENS (Transcutaneous Electrical Nerve stimulation), for treatment of headaches. It is hypothesized in this patent that the electrical stimulation prevents the constriction of arteries by stimulation of the muscle in the walls of the arteries, thereby preventing the dilation of capillaries, which dilation is a cause of headaches.
SU 1147408, the disclosure of which is incorporated herein by reference, describes a method of changing the distribution of blood flow in and about the liver, by applying electrical fields to arteries, varying the frequency of the field in synchrony with the cardiac rhythm.
U.S. Pat. No. 5,447,526, the disclosure of which is incorporated herein by reference, describes a transcutaneous electrical smooth muscle controller for inhibiting or decreasing the contraction of smooth muscle, especially uterine muscle. The controller, which is applied to the outside of the abdomen may also sense muscle contractions and effect inhibitory or stimulatory pulses unto the uterus as a whole, depending on the medical application, in response to sensed contractions.